This invention relates to a circuit interrupter and more particularly to a circuit interrupter provided with an automatic trip mechanism.
A conventional circuit interrupter to which the present invention pertains will be described in conjunction with FIGS. 1 to 5. FIG. 1 is a sectional side view of the conventional circuit interrupter, FIG. 2 is a partial enlarged sectional view of FIG. 1 and showing the ON position, FIG. 3 is a view similar to FIG. 2, but illustrating the OFF position, FIG. 4 is a view similar to FIG. 2, but illustrating the TRIP position, and FIG. 5 is a view similar to FIG. 2, but illustrating the electromagnetically operated position.
In these figures, the circuit interrupter comprises an electrically insulating housing 1 having a base 1a and a cover 1b. A stationary source side conductor 2 is mounted on the base 1a and has a stationary contact 3 secured thereon. Mounted in the housing 1 is an automatic trip unit 4 of a thermally responsive type, an electromagnetic type or an electronic type. A stationary load side conductor 5 is electrically connected to the automatic trip unit 4. A movable contact 6 is secured to a movable member 7 which is electrically connected to the automatic trip unit 4 through a flexible conductor 8 and a connector 9. The movable member 7 is supported by a contact arm assembly 10 comprising a first contact arm 10a connected to an operating mechanism 20 which will be described in more detail later, and a second contact arm 10b on which the movable member 7 is pivotally supported by a first pin 11. The first contact arm 10a and the second contact arm 10b are independently pivotally supported within the housing by a pivot pin 12. The first contact arm 10a has formed therein a first elongated guide hole 14 extending substantially in a direction of movement thereof. The second contact arm 10b has formed therein a second elongated guide hole 15 extending in a direction of extension thereof. A sliding pin 16 extends through the first and second guide holes 14 and 15 to limit the relative pivotal movement between the first and second contact arms 10a and 10b. The sliding pin 16 is biased toward a free end of the second contact arm 10b by a tension spring mounted between the sliding pin 16 and the first pin 11 pivotally connecting the movable member 7 to the second contact arm 10b. In order to provide a contact biasing force between the movable and the stationary contacts 6 and 3, a contact pressure spring 18 is disposed between the movable member 7 and the second contact arm 10b. An operating handle 19 is connected to the operating mechanism comprising a releasable cradle 20a having a stop pin 21 and a pair of toggle links 20b and 20c connected between the cradle 20a and the first contact arm 10a by pivot pins 22a and 22b. As is well known, an arc extinguisher 23 is disposed in such a way as to extinguish the arc generated between the separated contacts when they separate.
When the circuit interrupter is in the ON position shown in FIGS. 1 and 2, an electric current flows from the source side stationary conductor 2 to the load side stationary conductor 5 through the stationary contact 3, the movable contact 6, the movable member 7, the flexible conductor 8, the connector 9 and the automatic trip unit 4 in the named order. When the operating handle 19 is moved into the OFF position as shown by an arrow 24 of FIG. 2, the contact arm assembly 10 is lifted by the operating mechanism 20 so that the movable contact 6 together with the movable member 7 is moved away from the stationary contact 3 as shown in FIG. 3 to separate the contacts 3 and 6. At this time, since the sliding pin 16 is positioned in a recessed portion 14a of the guide hole 14 due to the biasing function of the tension spring 17, the second contact arm 10b is rotated about the pivot pin 12 into the opening direction by the operating mechanism 20 together with the first contact arm 10a until it abuts against the stop pin 21.
In the ON position shown in FIGS. 1 and 2, when an overload current flows through the circuit interrupter, the automatic trip unit 4 is actuated to release the cradle 20a of the operating mechanism 20 to allow it to rotate in a direction of the arrow 24 of FIG. 2. Then, the toggle links 20b and 20c of the operating mechanism 20 rotate the contact arm assembly 10 in a clockwise direction to separate the movable contact 6 from the stationary contact 3, thereby interrupting the overload current. This is the so-called tripped position. During this operation, since the sliding pin 16 is positioned within the recessed portion 14a of the guide hole 14 due to the tension spring 17 similarly to the OFF position shown in FIG. 3, the second contact arm 10b is rotated clockwise about the pivot pin 12 by the operating mechanism 20 together with the first contact arm 10a until it abuts against the stop pin 21.
When a large current such as a short-circuit current flows through the circuit interrupter in the ON position shown in FIGS. 1 and 2, an electromagnetic repulsive force generated between the stationary conductor 2 and the movable member 7 causes the movable member 7 to be immediately separated from the stationary conductor 2 as shown in FIG. 5. At this time, since the operating mechanism 20 does not allow the first contact arm 10a to be actuated because it has not yet been actuated, the second contact arm 10b rotates clockwise as shown by an arrow 26 in FIG. 2 about the pin 12 by moving the sliding pin 16 against the spring force of the tension spring 17 from the recessed portion 14a along the guide hole 14 until it abuts against an end portion 14b of the guide hole 14. An electromagnetic repulsive force generates very quickly upon the occurence of a short-circuit current and therefore the contact separation is achieved before the operating mechanism 4 is actuated, providing a high current limiting capability.
Immediately after the electromagnetic repulsive separation is achieved, the automatic trip unit 4 trips and rotates the first contact arm 10a to return the sliding pin 16 into the recessed portion 14a of the guide hole 14 to take up the tripped position shown in FIG. 4.
With the conventional circuit interrupter as above described, since the circuit interrupter is provided with the automatic trip unit 4 assembled within the interrupter housing, the circuit interrupter must be manufactured separately for each of the types of automatic trip unit, such as an electronic trip unit or a thermally responsive electromagnetic trip unit.